The present invention relates to a froth flotation process for the recovery of mineral values from base metal ores. More particularly, it relates to a new and improved process for beneficiating minerals by froth flotation incorporation a new class of depressants.
Certain theory and practice state that the success of a flotation process depends to a great degree on reagents called collectors that impart selective hydrophobicity to the mineral value which has to be separated from other minerals.
Certain other important reagents, such as the modifiers, are also largely responsible for the success of flotation separation of minerals. Modifiers include all reagents whose principal function is neither collecting nor frothing, but one of modifying the surface of the mineral so that a collector either adsorbs to it or does not. Modifying agents may thus be considered as depressants, activators, pH regulators, dispersants, deactivators, etc. Often, a modifier may perform several functions simultaneously.
In addition to attempts at making the collectors more selective for value minerals, other approaches to the problem of improving the flotation separation of value minerals have included the use of modifiers, more particularly depressants, to depress hydrous, layered silicates such as talc and other gangue minerals so that they do not float in the presence of collectors, thereby reducing the levels of non-value contaminants reporting to the concentrates. As has been mentioned above, a depressant is a modifier reagent which selectively prevents or inhibits adsorption of the collectors onto certain of the mineral particles surfaces present in the flotation slurry or pulp.
Hydrated silicates such as talc, i.e., is magnesium silicate, which, because of their crystalographic structure, *behave as a hydrophobic mineral when ground and slurried with water. The silicates therefore cause problems when associated with valuable minerals such as gold and platinum which are to be recovered by froth flotation. In the flotation of such hydrous, layered silicates as talc and pyrophyllite, depressants such as guar gum, starch, dextrin and carboxy methyl cellulose have been found to be useful commercially. Guar gum and carboxy methyl cellulose are the only two widely employed with the guar gum the most common depressant for talc by far. These conventional depressants, however, present a number of serious problems and have serious shortcomings attendant with their use. Guar gum, for example, is extremely difficult to dissolve and others are relatively expensive. Moreover, the conventional depressants are either non-selective or when used in sufficient quantities to provide good separation, provide economically unsatisfactory concentrates, i.e., the yield of value minerals is too low.
The beneficiation criteria for treating complex ores are maximum value metal and precious metals (if any) recovery and minimum contamination of the value concentrate by non-value hydrous, layered silicates such as talc. In many cases, these criteria cannot be met without seriously sacrificing value metals production or recovery. Therefore, there remains an urgent need for flotation reagents that can selectively depress reporting to the concentrate and concurrently provide economically acceptable recoveries of value minerals.
Unexpectedly, in view of the foregoing, it has now been discovered that hemicellulose is a very selective depressant for hydrous, layered silicates. The use of the hemicellulose of the present invention provides a substantial reduction in talc contamination in the mineral concentrates reporting to the smelters, and is more readily dissolved in water, i.e., it has a rapid hydration time, than guar gum and, because of its availability, it presents substantial cost reductions in the froth flotation of mineral values.